With the increasing consumption of fuel, such as coal, oil and natural gas etc., and the increasing depletion of energy resources reserve, looking for sustainable and environment-friendly energy technologies is imminent. Fuel cells have become a research hotspot in the world because of the advantages of high energy conversion efficiency, no pollution and no noise, etc.
Fuel cell technology includes proton exchange membrane fuel cell, solid oxide fuel cell, metal-air fuel cell and alkaline anion exchange membrane fuel cell. In terms of the current technology of proton exchange membrane fuel cell, its further development is constrained by noble metal catalysts with high cost and limited resources; the solid oxide fuel cell needs to be conducted under high temperature conditions; metal-air fuel cell has the advantages of abundant fuel supply, long storage life, low noise and non-precious metal catalysts as ORR catalysts; compared with proton exchange membrane fuel cell, none fuel permeation exists in alkaline anion exchange membrane fuel cell, thus none electrode potential decline is caused; in addition, non-Pt catalysts can also be used as ORR catalysts in alkaline anion exchange membrane fuel cell.
Non-Pt ORR catalysts are studied and explored by researchers in recent years. It was reported in literature (Phys. Chem. Chem. Phys. 9 (2007) 2654.) that silver is reasonably highly active and stable toward the ORR in alkaline solutions. Product of Ag/C catalysts in the field of alkaline anion exchange membrane fuel cell does already exist, while the ORR over potential for Ag/C was about 50-100 mV higher than Pt/C catalysts (reported in J. Electrochem. Soc. 152 (2005) D117), indicating the catalytic activity of Ag/C remains to be improved. Manganese oxide (MnyOx) with low cost is also a promising candidate for the ORR in alkaline media, while most ORRs on MnxOy undergo through a direct two-electron reduction process or a successive four-electron reduction process, resulting in a lower limiting current density.
According to the process in J. Phys. Chem. C 114 (2010) 4324, Ag/C is prepared by a method of two successive procedure: (1) reduction of AgNO3 in water phase, during which sodium citrate is selected as protective agent and sodium borohydride as reducing agent; (2) addition of Vulcan XC-72R as catalyst supports.
CN1396308A discloses a manganese oxide composite (MnO2—Mn3O4—Mn2O3) used as ORR catalysts in alkaline anion exchange membrane fuel cell and its preparation method thereof.
CN1266312C discloses an air electrode catalyst composed of manganese oxide (MnO2—Mn3)4/Mn2O3) wherein MnO2 is as the main catalyst, and Mn3O4 or Mn2O3 is as the assistant catalyst. MnO2 is obtained by heat decomposition of manganese nitrate solution adsorbed on carbon support, while Mn3O4 or Mn2O3 powder should be added to carbon support prior to manganese nitrate decomposition.
According to the process in Carbon 42 (2004) 3097; (Ag+MnO2)/SWNT is obtained by reduction of silver permanganate solution (AgMnO4) added with carbon nanotubes while hydrazine hydrate is as the reducing agent.
Comprehensive comparison of the above catalysts, the activity and stability of the catalysts and limiting current density of the battery still can't be satisfied simultaneously, which represents a further improvement is needed on the basis of the prior art.